Most probably, your Product Description contains empty Heading tags you've chosen to create accordion in app settings. It seems you've added a Heading, then removed the text, but the Heading tag is still there (but not visible in Shopify WYSIWYG editor as it contains no text), and app still recognizes it as a panel heading and creates panel for it.
To fix that please go to that Product in Shopify Admin, switch WYSIWYG editor to HTML View and remove empty Heading tags, like this:
If you'll have any difficulties, you may always ask our support team to check that for you. Just grant us access to your Store Admin and contact our support team by email email@example.com.